Pop it all behind a sliding door. A bit of ventilation needed so if close fitting doors then add a vent hole. Or be realistic and realise kids don’t shut doors.
A friend has a kitchenette in their basement rumpus and has plastic plates etc, think picnic, and kids are responsible for keeping it all clean. Personally you have a good kitchen downstairs, do you need a kitchenette upstairs. There are pros and cons and one of these might be how long you want your kids to live at home. Put that in either column,

I think your idea sounds great. The kids are never going to shut the door so ventilation won’t be a problem. My kids are slightly older and I’d love to have similar. It will be great when they’re grown up and come back to stay. I’d get it all done now. The sink could come in handy for craft activities. You could add the microwave and fridge later.

My kids are grown up now but when they were young teens we added 2 bedrooms and a study area in the attic, we never considered adding any kitchenette facilities for them as we thought it would be better if they and their friends to make an appearance in the kitchen family room every now and then. Our house was close to the city so we had a lot of kids spending the night before going on home in the morning.

siriuskey- yes i’ve had this thought myself and been told the same by my own mum - to give them and their friends more reason to show their face and know who their friends are. Just don’t want it to be the reason why they decide to hang at everyone else’s house instead of ours. Its hard to predict how it will go! Hence why I’m considering maybe putting the provision in and only doing it if I’m hounded about it. Power is easy, but capped off water pipes upstairs seems odd!

certainly put the plumbing in without seeing your plan could it be made into a shower, or just a tall cabinet with a door to enclose these.. I don't think that not having that space will turn them away, just make sure that you have FOOD that is the attraction, I agree with your mum

we had all the internal plumbing for a kitchen and adding a sink and taps later was easy for the kids to be used for crafts but i also think it was good to have the kids join the family for meals and so we had a chance to more than just meet their friends...i think i'd be more inclined to add a kitchenette to a parents retreat but can you share your plans so we can be more specific

siriuskey - yes the pipes can definately be enclosed by the “linen/robe” doors. I just wasnt sure if running pipes to a dead end was a doable thing. Am leaning more this way now. Plus there IS a bathroom sink right next door. Thanks for your perspective.

oklouise-Thanks I might look at doing what you did. There are many places I could put the kitchenette but its more a question of should I, I guess. We do have plenty of project, craft space downstairs too, so Im looking at this room as an “only when friends/cousins are over room”. Or maybe thats just wishful thinking and me hoping my kids dont get sick of hanging out with me! 😂

it definitely possible to include the pipes and drainage without having them connected to anything until you want to add a sink and taps and kids do eventually leave home but sometimes they come back and then it can be convenient to have some extra facilities